Our objectives are to evaluate the role of blood lipoproteins in ovarian function and to characterize lipoprotein metabolism by luteinized rat ovarian cells. Emphasis is placed on determining 1) whether ovarian cells have specific surface receptors which bind lipoproteins and thus facilitate their uptake and 2) whether gonadotropins, particularly prolactin and luteinizing hormone, regulate ovarian lipoprotein metabolism. In vivo studies in which blood cholesterol levels of immature gonadotropin-primed rats are lowered by treatment with 4-aminopyrazolo (3,4-d) pyrimidine, and in some cases replaced by infusions of purified lipoproteins, are carried out to evaluate the role of lipoprotein cholesterol in maintaining ovarian sterol stores and progestin production. The influence of lipoproteins on ovarian 3-hydroxy-3-methylglutaryl coenzyme A reductase and de novo sterol and steroid synthesis from 14C-acetate and 3H2O will also be studied. The binding affinity and binding specificity of 125I-labeled high density lipoproteins and low density lipoproteins from human and rat plasma will be studied with collagenase-dispersed cells from highly luteinized rat ovaries. Changes in these binding properties will be related to functional states of ovarian cells at various times after induction of luteinization. Binding, internalization and degradation of 125I lipoprotein will be followed in cultures of luteinized rat granulosa cells. The role of the lysosomal apparatus in degradation of lipoprotein will be assessed by exposing cells to lysosomotropic agents such as chloroquine. Utilization of lipoprotein bound 3H-cholesterol for steroid production will be studied by monitoring synthesis of 3H-progestins by cultured granulosa cells. Effects of gonadotropins on these processes will also be evaluated. Our studies should define mechanisms by which ovarian cells acquire and utilize cholesterol for steroidogenesis.